The need for effective therapeutic treatment of patients has resulted in the development of a variety of pharmaceutical formulation delivery techniques. One traditional technique involves the oral delivery of a pharmaceutical formulation in the form of a pill, capsule, elixir, or the like. However, oral delivery can in some cases be undesirable. For example, many pharmaceutical formulations may be degraded in the digestive tract before they can be effectively absorbed by the body. Inhalable drug delivery, where an aerosolized pharmaceutical formulation is orally or nasally inhaled by a patient to deliver the formulation to the patient's respiratory tract, has proven to be a particularly effective and/or desirable alternative. For example, in one inhalation technique, an aerosolized pharmaceutical formulation provides local therapeutic relief to a portion of the respiratory tract, such as the lungs, to treat diseases such as asthma and emphysema. In another inhalation technique, a pharmaceutical formulation is delivered deep within a patient's lungs where it may be absorbed into the blood stream. Many types of aerosolization devices exist including devices comprising a pharmaceutical formulation stored in or with a propellant, devices that aerosolize a dry powder, devices which use a compressed gas to aerosolize a liquid pharmaceutical formulation, and similar devices.
One conventional type of aerosolization device is commonly referred to as a metered dose inhaler (MDI), which is sometimes referred to as a pressurized metered dose inhaler (pMDI). In a metered dose inhaler, a pharmaceutical formulation and a propellant are stored in a canister. In one version the pharmaceutical formulation is suspended within the propellant, and in another version the pharmaceutical formulation is dissolved in the propellant. In either version, a valve may be actuated so that a metered amount, or dose, of the pharmaceutical formulation is aerosolized in a manner where is may be inhaled by a user. The canister may contain one or more doses of the pharmaceutical formulation and generally contains sufficient amounts of propellant to allow for several actuations. Traditionally, the propellant comprises one or more chlorofluorocarbon compounds. However, non-chlorinated propellants, such as hydrofluoroalkanes, that are believed to be more environmentally friendly are proving to be a desirable alternative.
Though generally well accepted and inexpensive, metered does inhalers have certain drawbacks. For example, the amount of pharmaceutical formulation that may be aerosolized during an actuation is limited. In addition, it can often be difficult to control the efficiency of delivering large quantities of a pharmaceutical formulation using a metered dose inhaler.
Therefore, it is desirable to be able to aerosolize a pharmaceutical formulation in an efficient manner. It is further desirable to provide an improved metered dose inhaler that is capable of effectively aerosolizing a large quantity of a pharmaceutical formulation. It is still further desirable to provide an improved metered dose inhaler with improved aerosolization efficiency and reproducibility.